The invention relates to a method for test pressing tablets consisting of at least two layers.
As is generally known, rotary tablet presses comprise a rotor driven by a rotary drive, said rotor has a die plate, upper punches and lower punches, which are guided in suitable guides, and a control cam system. Moreover, at least one press station is provided, which is usually comprised of an upper pressure roller and a lower pressure roller, by means of which upper punches and lower punches are pressed into the die, as they pass the press station. Usually, two pairs of pressure rollers are provided for pre-pressing and final pressing of the material. Finally, a filling device is provided, by means of which the material to be compressed is filled into the die bores. The rotor is set in rotation continuously, whereby the filling device permanently fills material into the associated die bores and the associated lower punch ejects the finished, pressed tablets out of the die bore, from where they are directed into a channel by means of a wiper.
It is also known to produce multi-layer tablets with such a rotary tablet press. The multi-layer tablets are produced during one revolution of the rotor, whereby one filling device and one pressure roller arrangement (press station) are provided per layer. If for example a three-layer tablet is manufactured, three filling devices in a spacing of 120° degrees are provided as well as three press stations with at least one pair of pressure rollers between the filling devices.
Moreover, it is known to produce so-called coated tablets by means of a rotary press. The term “coated tablet” usually identifies a two-layer tablet, in which between the layers a core is disposed. After filling in and pressing of the first layer, a core of a different material is placed on the first layer and thereon, a second layer is filled in. When producing such coated tablets, one can proceed in different ways. It is possible to fill in the first layer and to perform the pressing not before the second layer has also been filled in. In the alternative, the first layer can be pressed before the core is inserted. Thereafter, the compression of both layers with the core is performed. Finally, it is also possible to press the core to a certain extent into the first layer following insertion. This can be accomplished with the upper punch in the press station as well. The described processes can be executed during one revolution of the rotor.
It is known to provide such a tablet press with a measurement device, which records important data during production and further processes the data in an operating computer. These data comprise the rotational speed of the rotor, the maximum pressing forces in the press station and—if applicable—the course of the pressing force in the press station, namely associated to the individual pairs of punches. By means of retrospective measurement of the ejected tablets with respect to weight, thickness and hardness, it is determined whether the desired parameters were achieved. If not, the filling quantity, pressing force or other parameters need to be adjusted. Devices and methods for controlling or regulating of the tablet presses in order to achieve optimal results are known from the prior art.
During the development of tablets, among other things, the compression characteristics of the material to be compressed are determined. To this end, at the beginning, only very little quantities of the product are available, which may be very costly and time-consumingly to produce and which may require costly material, so that the product losses during the pressing process need to be minimized. It is known to perform test pressings with special laboratory presses. In most cases, smaller eccentric presses are used, which can manufacture one tablet in each pressing process. It is a disadvantage that these laboratory presses have a different pressing behavior than rotary tablet presses, which are used for production. By nature, test pressings with a production rotary press have the advantage that the data determined in the tests can be transferred directly to the production. A disadvantage is that a filling device as is normally used needs to be filled permanently and evenly, in order to have a sufficient volume with a basic amount of pressing material, even if only a small number of tablets is produced. From DE 103 19 024 B3 a method for test pressing tablets with a rotary tabletting machine has become known, wherein a pair of selected punches for a single pressing is moved automatically into a filling position, and at least one die is filled with the material to be compressed. Afterwards, the rotor is set in rotation and is accelerated such that it has the desired production speed in the press station. After one rotation, the rotor is stopped in the filling position. During the revolution of the rotor, signals or courses of signals of the measuring points are recorded and transferred to a computer for display and analysis.
The conditions that have been described in combination with test presses for tablets, occur in an aggravated manner during test pressings of multi-layer tablets or coated tablets, respectively. As has been mentioned, a rotary press for multi-layer tablets needs several filling stations and press stations, dependent upon the number of layers of the tablet.
Therefore, the invention is based on the problem to provide a method for test pressing of multi-layer tablets or coated tablets, respectively, which can on the one hand be performed under production conditions, and on the other hand requires only little amounts of pressing material.
According to the inventive method, the rotor is provided with only one pair of punches and by means of the operating computer and control computer, the rotor can be moved into a defined filling position, in which the pair of punches is placed in this position. The lower punch is disposed in a first filling position, while the ejection cam is disposed in an inactive position. The die is filled with the material for the first layer.
It shall be mentioned that the pressure rollers in the press station have taken a first pressing position. The adjustment of the cams and of the pressure rollers is accomplished by means of suitable adjustment drives, for example a hydraulic, pneumatic, or electromechanical drive. Afterwards, the rotor is rotated by one revolution, until the pair of punches has again reached the filling position. Thereby, a pressing of the first layer of the multi-layer tablet has been performed. Because the ejection cam was located in an inactive position, the first layer is not ejected, but remains in the die bore. After the filling position has been reached again, the filling cam is moved in a position in which a dosed filling of the second layer of the multi-layer tablet can be performed. Before a second revolution of the rotor, the pressure rollers are moved into a second pressing position. Moreover, the ejection cam is moved into an ejecting position, when only a two-layer tablet shall be produced. During the second revolution of the rotor, in this way the second layer of the tablet is pressed and the two-layer tablet is ejected by the associated lower punch and the ejection cam. Accordingly, n-revolutions of the rotor are required in order to produce a multi-layer tablet with n-layers, that is one revolution per layer, each with an individual adjustment of the cams and the pressure rollers.
If a three-layer tablet is produced, three revolutions of the rotor with the steps described above are required. Not until the third revolution, the ejection of the three-layer tablet by means of the lower punch is performed.
During the specific revolutions of the rotor, the signals of the single measuring points, for example for the pressing force, are recorded and transferred to an operating computer for display and analysis. The signals measured serve for example for a determination of the compression characteristics of the pressing material.
By means of a suitable computer control, it is also possible to produce automatically several multi-layer tablets in a row, wherein the described process parameters can be adjusted and modified automatically following each revolution. The number of layers of the tablet is theoretically unlimited.
The method for producing a coated tablet works similar to the method according to patent claim 1. At first, a first layer is filled in and preferably “pre-pressed”. At the next stop following one revolution of the rotor, the core is inserted. This core may be pressed a bit into the lower layer by means of the upper punch. However, it is also possible to first place the core and then to fill in the second layer into the filling station, at the same stop of the rotor. Afterwards, the rotor executes one revolution, during which both layers together with the core are compressed to the final tablet. Thereafter, as has been described above, the ejection of the coated tablet is performed.
The filling-in of the material to be compressed and of the core can be performed by hand. However, it is also possible to provide a filling device. To this end, one embodiment of the invention is provided with a filling device with is rotatable about a vertical axis, said filling device exhibiting one chamber for receiving a layer material per layer of the multi-layer tablet. When the filling device is rotated, by means of for example a rotary drive, each time one filing outlet of a chamber is aligned with a die bore in the filling position.
The inventive method has a number of advantages. Test pressings could be performed with a rotor configured with only one pair of punches and with or without blank dies. Changeover times for different materials to be compressed or different types of punches, respectively, are very short. There is only little formation of dust during the test pressings, because only little amounts of material are used.
The product losses are very small, because each time only one die bore is filled with the layer material. All settings relevant for the process can be adjusted and tested in the test pressings: Rotational speed of the rotor, pressing force in the press station, thickness, hardness and weight of the tablets, and so on. The data determined in the test pressings and the different settings can be transferred directly to a production rotary press, for example the rotational speed, the pressing force, thickness, hardness and weight of the tablets, and so forth. The measurement data for each pressing process are available directly and can be displayed, analyzed and stored together with all data relevant for the process in the operating computer.